Or more accurately how to turn people off running with headphones. Amazingly before the invention of headphones, people still occasionally managed to run. Granted they were mostly mad and thus could already hear voices in their heads, but nevertheless it was considered possible.
The MAF formula really is bullshit though. Anything using an arbitrary number based on age is by default going to be bollocks. That's not to say that people can't get great results - they can, but only if - A) Their HR happens to fall into a range that the formula makes sense for. B) They have a massive amount of spare time required to make low intensity exercise make sense.
I think you might be underestimating how hard your 18 minute target might be to achieve. I'm a very mediocre runner, but could pass that 1.5 mile test, but I'd never ever ever ever be able to do an 18 minute 5K.